Alpha-carotene & cancer

Call it the beta-carotene quandary. Researchers are scrambling to figure out why foods rich in beta-carotene seem to reduce the risk of lung cancer while high doses of beta-carotene supplements seem to increase the risk.

One theory--that massive doses of beta-carotene keep people from absorbing other substances in fruits and vegetables that may be the real protectors--now has new support from a study from the National Cancer Institute in Bethesda, Maryland.

Regina Ziegler and co-workers analyzed the diets that 763 men recalled eating before they were diagnosed with lung cancer. She compared the diets to those of 564 similar men with no cancer.

The results: Lung cancer was more closely associated with a low intake of alpha-carotene than with a low intake of beta-carotene. Among the men who were current or recent smokers, a diet poor in beta-carotene increased the risk of lung cancer by 60 percent, while a diet poor in alpha-carotene roughly doubled the risk.

Alpha- and beta-carotene usually occur in the same foods. Only seven of the men had frequently eaten foods that are especially rich in beta-carotene (like spinach and other leafy greens) and had infrequently eaten foods that are rich in both carotenes (like carrots and sweet potatoes). All seven got lung cancer.

"It is premature to conclude that alpha-carotene is protective in humans," says Ziegler. "The most rational way to reduce lung cancer risk is to eat a variety of vegetables and fruits and, most important, to not smoke."